A wobble type compressor having a wobble plate and a plurality of pistons slidably provided within cylinders and functionally connected to the wobble plate is used as the compressor for automotive air conditioners. It has been known for the wobble type compressor that the inclining angle of the wobble plate is varied in order to change the reciprocating stroke of the piston (U.S. Pat. No. 3,861,829).
Though such a type of variable volume wobble compressor can vary the volume in accordance with the inclining angle of the wobble plate, the inclining angle of the wobble plate is hard to controll. Since the inclining angle of the wobble plate is controlled in accordance with the pressure within a housing, and since it is difficult to change the pressure within the housing, conventional type of the variable volume wobble type compressor is difficult to control accurately. Namely, there must exist some time lag between the timing when the control pressure is introduced into the housing and the timing when the wobble plate inclines the desired inclining angle, and such a time lag cannot be estimated accurately.
Therefore, a positioning sensor which can sense the position of the wobble plate is desired.
Since the conventional type of positioning sensor using a magnet can sense only a small distance (3 mm for example), the conventional type sensor cannot be used for sensing the position of the wobble plate. Another type of positioning sensor using a photosensor is also hard to use with the compressor, because the photosensor must be provided within the housing and because the operation of the photosensor is hindered by the lubricant oil or any other foreign object within the housing.